The methods of x-ray diffraction are being used to determine quantitative aspects of metalloporphyrin stereochemistry. Metalloporphyrin derivatives to be studied or studies which are currently in progress include the four-coordinate chromium(II) and zinc(II) derivatives. These studies extend our data on the correlation of electronic configuration with molecular structure. Other metalloporphyrins being studied include iron porphyrin systems with various different axial ligands. Iron derivatives with unusual magnetic properties are also being pursued. Work is also being continued on the synthesis and structural characterization of a series of nitrosyl-metalloporphyrins. BIBLIOGRAPHIC REFERENCES: J.F. Kirner, W. Dow, and W.R. Scheidt. Molecular stereochemistry of two intermediate-spin complexes. Iron(II) phthalocyanine and manganese(II) phthalocyanine. Inorg. Chem., 15, 1685 (1976). J.F. Johnson and W.R. Scheidt. Remarkably different structures of two metalloporphyrins containing M2O3 4 ion units. J. Am. Chem. Soc., 99, 294 (1977).